1. Field of the Invention
This invention relates generally to synthetic aperture radar (SAR) including adaptive signal processing, and more particularly to a foliage penetrating SAR mapping system which operates in the UHF frequency band.
2. Description of Related Art
The principle of synthetic aperture radar (SAR) mapping is well known and comprises a radar system, which is carried by an aircraft traversing a particular area of interest and is typically used for ground mapping. The frequencies and accordingly the wavelengths normally used by such radar systems such as Ku-band, are substantially if not entirely blocked by ground foliage, i.e. trees and brush.
While there is a current need for a compact foliage penetrating radar, relatively long wavelengths, e.g. UHF, are required and must be combined with high resolution which require wide bandwidth. Such a capability would be most welcome in applications requiring reconnaissance or destroy missions to be performed by unmanned aircraft. Such a mission could reveal concealed equipment e.g. tanks, trucks and weaponry which is at present prevented from being detected by SAR mapping radar equipment operating, for example, in the Ku-band. While one such Ku-band SAR system radar is presently known and which is mounted in an aircraft known as an unmanned air vehicle (UAV), there is a limited space, particularly for the antenna in a UAV. In order for such an aircraft to act as a platform for a UHF SAR, an antenna is required that operates across a very large fractional bandwidth and must be small and light enough to fit in the space presently allocated for the existing antenna system.
At present there is no known antenna or SAR system that will fit in the nose portion of a relatively small unmanned reconnaissance vehicle that has the capability of penetrating foliage so as to detect targets which are obscured by trees, underbrush and other types of foliage.